A method and apparatus for ferrous object and/or magnetic field detection are provided. Embodiments can improve magnetic resonance imaging (MRI) safety and increase the safety of MRI facilities. Embodiments can detect a given magnetic field strength around a MRI machine and alert users to the field's presence. In an embodiment, the magnetic field warning system can rely on a single badge that warns its user. In another embodiment, the badge can utilize an RFID system. The RFID system can turn the badge on when it enters the MRI room and off when it leaves the MRI room. In another embodiment, a badge with a rechargeable battery and charger can be utilized with or without an RFID tag. The subject badges or other detection devices can be worn by a person, located on or near a ferrous object, embedded in clothing, or located in other positions convenient to a user.